Conventional rotary drilling is performed using a rotary table, which includes a motor mounted on or below the derrick floor for rotating the table, and a Kelly which rationally connects the table to a drill string. Alternative drilling systems have been increasingly used, in which the pipe string drive has been modeled after a drilling unit, including a section of pipe connectable to the upper end of the drill string, and a motor for rotating the upper pipe section to turn the string. In recent years, rotary table drilling units are being replaced with these direct drive drilling units (e.g. top drives, kelly drives).
A typical direct drive drilling unit includes a motor drive assembly and a pipe handling assembly. The drive assembly includes a motor connected to the drill string by a cylindrical drive sleeve drilling extending downwardly along the centerline of the well from the drill motor. A direct drive unit is normally suspended from a travelling block for vertical travel supported by a derrick assembly. The drilling unit can be mounted on a carriage connected to a pair of vertical guide rails secured to the derrick.
Drilling is accomplished by the powered rotation of the drill string by the drill motor. The drill string is composed of loose drill string elements with a cutting tool or a bit fixed on the end of a drill string. The drill string elements consist mainly of a piece of pipe, which is provided on either side with fixing elements (e.g. threads) for connecting together adjacent pipe segments. This entire powered drilling assembly can then be moved upwardly and downwardly, with the string, to drive the string directly, without requiring a Kelly and Kelly bushing type connection. The cutting tool and/or drill bit can be threadably connected to the lower end of the drill string which, through the rotational energy supplied by the drill motor, cuts through the earth formation and deepens the well.
During drilling operations, the drilling tool is guided into and through earth formation by using a drill string. Additional drill string elements (e.g. segments of drill pipe) are repeatedly added to the upper end of the drill string, so that the drilling tool can extend ever further down-well. Assembling such a drill string takes a relatively long time, especially when a large number of pipe sections are assembled in the course of drilling a deep well.
Additionally, when it is necessary to perform maintenance and/or repairs on a drill string or tools attached thereto, the amount of time required for such an undertaking increases substantially as the depth of a well increases. For example, as the well is drilled, the bit becomes worn and the cutting elements thereof must periodically be replaced. To access a drill bit, the entire drill string must be removed from the well. Other types of damage and/or wear can also require raising the drill string. During the hoisting operation, the drill string is at least partially disassembled (e.g. the drill string is often separated into sections of three joined pipe segments). The time required to raise and disassemble can therefore be substantial.
As such, when replacement of the bit or other types of repairs, replacement, and/or remedial operations become necessary, at least a portion of the drill string is removed from the well, pulled above the derrick floor, and moved to a pipe storage rack on the derrick or similar location. Subsequent drill string elements are pulled from the well, exposing the next pipe section above the floor, which is similarly removed. This sequence, usually referred to as tripping out, is continued until the necessary portion of the drill string, which can include the entire drill string, is removed from the well. After replacement of the drill bit and/or completion of other remedial operations, the drill string is then reassembled, e.g. tripped in, by reconnecting and lowering all of the pipe sections previously removed.
As drilling depths and the length of wellbores increases, drilling efficiency must be increased and/or new techniques developed to offset the costly day rates for retaining and operating equipment capable of addressing deep well applications. To prevent a great deal of time from being lost when assembling or dismantling a drill string, a need exists for devices and methods that decrease the time required to disconnect drill string segments and raise a drill string.
A need also exists for apparatus and methods that can quickly and continuously prepare pipe members for connection, while concurrently performing drilling operations.
A further need exists for a drilling apparatus having multiple pipe hoisting and driving capabilities available and/or proximate to one another for the purpose of connecting and/or lowering a pipe segment, while a second pipe segment is engaged and prepared for connect.
A need exists for efficiently communicating drilling fluid into the drill string without requiring deactivation of the drilling fluid pump while successive drilling string segments are being connected.
Embodiments usable within the scope of the present disclosure meet these needs.